We propose to develop a gel based approach that would display most of the single base substitution mutations present in any mRNA expressed in a cell type. The method would permit recovery of bands for sequencing and identification of the sites of mutation. We describe the application of this approach to the detection of somatic mutations in malignant cells. In Phase 2 we propose to apply the method to malignant melanomas, colon carcinoma, acute Myelocytic leukemia and myelodysplasia. In addition, we propose protocols for improving the sensitivity of the method, for extending it to small tissue samples, and for detecting mutations in a small fraction of cells in a sample.